There are two leading methods for producing three dimensional images. One method use triangulation. The other method is based on Time-of-Flight measurements.
Triangulation is any kind of distance calculation based on given lengths and angles, using trigonometric relations.
Triangulation with two parallel cameras, or stereo triangulation, may be performed based on parameters like, for example, distance between the cameras, focal length of the cameras, spatial angles of the Line-of-Sight (LOS) from the imaged object to each camera and/or other suitable parameters. This kind of triangulation is sometimes called “Passive Triangulation”. This kind of triangulation may require additional means to determine which points in the images received by the two cameras correspond to the same actual point.
Other form of triangulation may require at least one camera and a light source which may create a pattern on the object or alternatively scan the object angle by angle with a stripe of radiation. The calculation may base on the spatial angle of the LOS from the imaged object to the camera, for each scanning angle. This kind of triangulation is sometimes called “Active Triangulation”.
In the method based on the Time-Of-Flight (TOF) principle, the depth information may be captured by emitting pulses of radiation to all objects in the scene and sensing the reflected light from the detected objects. The pulses of radiation may be obtained by switching the radiation source on and off. All objects in the scene may then be arranged in layers according to the amount of radiation sensed by the depth pixels in the camera in each pulse period, which may be translated to distance information, providing the depth information in real time as standard black and white video where the grey-level correlates to relative distance. In this method, color data may be provided, for example, by using a normal color imaging sensor.
TOF depth sensors may also be based on detection of phase shift in the radiation reflected from the detected objects. The radiation pulses may be given a signal shape with a frequency, for example, a square wave or a sinusoidal wave. The light reflected from the object arrives at the sensor with a phase shift. The phase shift of the radiation signal shape as received at the sensor may be measured, and the distance between the object and the sensor can be calculated there from. In this method, the distances to objects differing by 360 degrees of phase shift may not be distinguishable. It is possible to overcome this shortcoming by using multiple frequencies in the radiation signal.
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